1. Field of the Invention
Aspects of the present invention relate to a phase controlling device, a fuser controlling device having the same, and a phase controlling method. More specifically, an aspect of the present invention relates to a phase controlling device using less circuit elements, thus simplifying the configuration of the device and reducing manufacturing costs, a fuser controlling device having the same, and a phase controlling method.
2. Description of the Related Art
An image forming apparatus is an apparatus printing images corresponding to input image data on a recording medium, such as paper, transparency, etc. These apparatuses include printers, photocopiers, facsimiles, multi-function printers and so on.
In general, the image forming apparatus includes a heat generating device enabling normal print jobs and a device for maintaining the heat of the heat generating device at a certain temperature. In particular, a fuser which functions to fix toner images on paper under heat and pressure needs a fuser controlling device for keeping the surface of the fuser at an appropriate target temperature to fix toner images on paper, a transparency, etc.
Such a fuser controlling device is generally operated by a phase controller which controls an applied AC power. To carry out the phase control, the fuser controlling device requires a phase controlling device that detects a difference between a target or reference temperature of the fuser and practical temperature, i.e., present or actual temperature, of the fuser, generates an error signal corresponding to the detected difference between target temperature and present temperature, and outputs a phase control signal having a variable pulse width based on the error signal generated.
Moreover, in order to output such a phase control signal having a variable pulse width, the fuser controlling device needs a pulse generation unit that outputs predetermined pulse signals.
FIG. 7 is a block diagram of a phase controlling device according to a conventional example, FIG. 8 is a circuit diagram of an example of a signal generation unit shown in FIG. 7, and FIGS. 9A-9D and 10A-10D are drawings explaining a driving method of a fuser controlling device provided with the phase controlling device in FIG. 7.
Referring to FIGS. 7 and 8, the phase controlling device 10 according to a conventional example includes a pulse generation unit 20, a signal generation unit 30, and a PWM controller 40.
The pulse generation unit 20, as shown in FIGS. 9A-9D, generates a sawtooth wave pulse signal Vramp′ that changes in time during a half period of AC power.
The signal generation unit 30 senses actual temperature of a fuser included in an image forming apparatus (not shown), and receives from a temperature sensor (not shown) a temperature detection signal Vact_temp′ having a predetermined voltage level according to the sensed temperature. In addition, the signal generation unit 30 receives a reference temperature signal Vref_temp′ corresponding to a predetermined target or reference temperature of the fuser that has been set to a main controller of the image forming apparatus or the PWM controller 40.
The signal generation unit 30 calculates a difference between the inputted target or reference temperature and the present temperature, and outputs an error signal Verr′ having a voltage level corresponding to the temperature difference therebetween.
For instance, as shown in FIG. 8, the signal generation unit 30 can include a subtractor circuit. If the actual temperature of the fuser is relatively higher than the reference temperature, an actual temperature detection signal Vact_temp′ and a reference temperature signal Vref_temp′ are subtracted through the subtractor circuit, and the error signal Ver′, similar to a second error signal Verr2′ shown in FIGS. 9A-9D, having a relatively low voltage in inverse proportion to an increase in temperature of the fuser is outputted.
Meanwhile, if the actual temperature of the fuser is relatively lower than the reference temperature, an actual temperature detection signal Vact_temp′ and a reference temperature signal Vref_temp′ are subtracted through the subtractor circuit, and the error signal Verr′, similar to a first error signal Verr1′ shown in FIGS. 9A-9D, having a relatively high voltage level in inverse proportion to a decrease in temperature of the fuser is outputted.
The PWM controller 40 receives the sawtooth wave pulse signal Vramp′ outputted from the pulse generation unit 20 and the error signal Verr′ outputted from the signal generation unit 30, compares voltage levels of both signals, and outputs a phase control signal having a pulse width corresponding thereto.
To this end, the PWM controller 40 may have a comparator capable of comparing the voltage level of the error signal Verr′ with the voltage level of the sawtooth wave pulse signal Vramp′.
At this time, the PWM controller 40 outputs, as depicted in FIGS. 9A-9D, a phase control signal Vphase′ having a high phase, only if the voltage level of the error signal Verr′ is higher than the voltage level of the sawtooth wave pulse signal Vramp′ according to the comparison result of the voltage levels between the error signal Verr′ and the sawtooth wave pulse signal Vramp′.
Therefore, as described above, if the actual temperature of the fuser is relatively higher than the reference temperature, an error signal Verr outputted from the signal generation unit 30 may have the voltage level of the second error signal Verr2′; while if the actual temperature of the fuser is relatively lower than the reference temperature, the error signal Verr may have the voltage level of the first error signal Verr1′. Accordingly, as shown in FIGS. 9A-9D, a pulse width of the phase control signal Vphase′ generated when the second error signal Verr2′ is outputted is relatively narrower; while a pulse width of the phase control signal Vphase′ generated when the first error signal Verr1′ is outputted is relatively broader.
In addition, although not shown in the drawing, when the image forming apparatus (not shown) is started, or restarted from the standby mode that restricts the operation of the fuser to reduce power consumption by not printing, a charging element like a capacitor is provided to the PWM controller 40 to block or prevent transient current flow to the fuser at the time of operation. As shown in FIGS. 10A-10D the signal generation unit 30 outputs the error signal Verr′ that increases gradually.
The PWM controller 40 compares the sawtooth wave pulse signal Vramp and the error signal Verr′ received, and outputs a phase control signal Vphase′ having a gradually increasing pulse width. By this phase control signal Vphase′, a phase of alternating current power AC is controlled and a phase controlled alternating current power AC_IN is applied to the fuser. In this way, it is possible to prevent transient current flow to the fuser at the beginning of its operation.
The fuser controlling device provided with the above-described phase controlling device controls phase of the applied alternating current power AC by using a phase control signal having a variable pulse width according to the actual temperature, and applies the phase controlled alternating current power AC_IN to the fuser. Accordingly, if the time for impressing AC_IN is relatively long, exothermic temperature of the fuser increases; while if the time for impressing AC_IN is relatively short, exothermic temperature of the fuser decreases, keeping the reference temperature.
Therefore, in order to output a phase control signal using a sawtooth wave pulse that decreases with the passage of time, the phase controlling device 10, as shown in FIG. 8, includes the signal generation unit 30 to which a temperature detecting signal Vact_temp′ with its polarity reversed is applied. Then, a subtractor is realized using a bipolar power supply +V and −V for OP-AMP of the signal generation unit 30.
However, to build such a subtractor, a circuit for generating a reversed polarity voltage as shown in the drawing is additionally needed. This consequently makes it difficult to attain integration and increases the cost of manufacture.
Another problem with the conventional device is the cost of manufacturing the phase controlling device needed for generating a sawtooth wave pulse.
That is, although the phase controlling device 10 having the pulse generation unit 20 and the signal generation unit 30 is formed into a single chip exclusive for phase control, it increases the cost of manufacture of such structure and further the cost of manufacture of a fuser controlling device having the same and an image forming apparatus having all these are increased.